The present invention relates to an arrangement for the recognition of obstacles for motor vehicles, with a transmitter and a receiver for electromagnetic radiation which are directed onto an examination area (close range) that commences in direct proximity.
Such arrangements are generally known. For example, visible light which is emitted from a laser light source serves as electromagnetic radiation. In addition thereto, the radiation may also be invisible and may stem, for example, from a source for infrared light.
It is desirable with such arrangements to cover as large as possible an examination area. This can take place best in such a manner that the transmitter and receiver transmit and receive their radiation along the same path. In the ideal case, for example, in the case of a laser, the output and input optical systems may coincide. As an approximation, however, they may also be arranged directly adjacent one another.
However, problems occur with such an arrangement under special atmospheric conditions. Among those is to be understood the case of water droplets which appear in large number between an obstacle to be detected and the vehicle. Typically, this is the case during fog or strong rain showers. These water droplets then reflect the electromagnetic radiation and render more difficult or prevent the recognition of an obstacle.
The present invention is concerned with the task to provide with low constructive expenditures an arrangement of the aforementioned type which, in the case of atmospheric disturbances, such as fog or strong rain, nonetheless permit the recognition of an obstacle.
The underlying problems are solved according to the present invention by a second receiver which, together with the transmitter, is directed onto a second examination range (distant range) which commences at a considerably larger distance than the close range.
As a result of the enlargement of the distance of the examination area, the reflection at the water droplets in the close range no longer plays any role. This reflection corresponds approximately to the reflection at an obstacle that is located relatively close to the vehicle. Added thereto is a further circumstance. The greater distance of the examination area is usually accompanied with a reduction in size of this area. However, the number of the water droplets capable, respectively, leading to a disturbing reflection, is also correspondingly reduced. The reduction of the number of fog droplets now leads to a reduction of the disturbing reflections which is considerably stronger than the reduction of the number of fog droplets. This can be traced back to the fact that the electromagnetic radiation is scattered also several times at these water droplets.
Further improvements of the present invention are obtainable by additional features. A considerable improvement in connection with the recognition of obstacles both in the proximity of the motor vehicle as also at the distance can be achieved if the second receiver together with a second transmitter is also directed to a further close range and the second transmitter together with the first receiver is directed to a distant range and the transmitters/receivers are adapted to be alternately interconnected cross-wise. As the two close areas are not coincident as a rule, obstacles can be recognized therewith at least approximately gaplessly within this area. The same is also true for the distant area. A noticeable improvement both as regards the range as also the width of the examination area results therefrom.
In contrast to a manual switching, which is also possible, an automatic switching to the cross-wise interconnection of transmitters and receivers can be obtained according to the present invention, for example, in conjunction with turning on a fog light or as a function of the intensity of the radiation reflected from the close range. These characteristics provide safe indicia for the necessity of the switching.